Re: [PATCH v3 16/23] Documentation: userspace-api: iommufd: Update vQUEUE

Bagas Sanjaya
2025-05-02T07:33:33Z

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On Thu, May 01, 2025 at 10:29:58PM -0700, Nicolin Chen wrote:
> On Fri, May 02, 2025 at 10:50:07AM +0700, Bagas Sanjaya wrote:
> > On Thu, May 01, 2025 at 04:01:22PM -0700, Nicolin Chen wrote:
> > > +- IOMMUFD_OBJ_VQUEUE, representing a hardware accelerated virtual queue, as a
> > > + subset of IOMMU's virtualization features, for the IOMMU HW to directly read
> > > + or write the virtual queue memory owned by a guest OS. This HW-acceleration
> > > + allows VM to work with the IOMMU HW directly without a VM Exit, i.e. reducing
> > > + overhead from the hypercalls. Along with this vQUEUE object, iommufd provides
> > > + user space an mmap interface for VMM to mmap a physical MMIO region from the
> > > + host physical address space to the guest physical address space, allowing the
> > > + guest OS to control the allocated vQUEUE HW. Thus, when allocating a vQUEUE,
> > > + the VMM must request a pair of VMA info (vm_pgoff/size) for an mmap syscall.
> > > + The length argument of an mmap syscall can be smaller than the given size for
> > > + a partial mmap, but the addr argument of the mmap syscall should never offset
> > > + from the returned vm_pgoff, which implies that an mmap will always start from
> >
> > Did you mean never be offset from returned vm_pgoff?
>
> Yes. Will fix this.
>
> > > + the beginning of the physical MMIO region.
> > > +
> >
> > Confused...
>
> Meaning that VMM should just use the given vm_pgoff as is, without
> adding any offset to the vm_pgoff.

Understood, thanks!

--
An old man doll... just what I always wanted! - Clara

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